1. Field of the Invention
The present invention relates to a multi-lamp driver, and in particular to a driver for discharging lamps to balance currents flowing through the lamps.
2. Description of the Related Art
Current display devices, such as liquid crystal display (LCD) devices, require lamps with high efficiency and light shape to serve as backlight units. Cold cathode fluorescent lamps (CCFLs) are usually used in LCD device. As the size of display devices increases, single lamp backlight units become inadequate. A backlight unit with a plurality of lamps, however, can provide enough brightness for a large display device.
FIG. 1 is one conventional multi-lamp driver. The driver comprises a driving circuit 11, a transformer 12, capacitors C1 and C2, a balance circuit 13, and lamps 151 and 152. The transformer 12 is composed of a primary winding set 121, a secondary winding set 122, and a magnetic core 123. The driving circuit 11 provides a low-voltage signal to the primary winding set 121 of the transformer 12, and the secondary winding set 122 thereof inducts a high-voltage signal to drive the lamps 151 and 152. Currents flowing through the lamps 151 and 152 are different due to resistance of wires or stray capacitance. The different currents result in non-uniform brightness of the lamps 151 and 152, reducing image quality. The balance circuit 13 is thus used to balance the different currents flowing through the lamps 151 and 152.
FIG. 2 is another conventional multi-lamp driver. To describe the driver of FIG. 2, the elements of the driver in FIG. 2 same as those of the driver in FIG. 1 are identified with the same reference numerals. A balance circuit 23 of the driver in FIG. 2 is coupled to a ground and between the lamps 151 and 152, different from the balance circuit 13 of the driver in FIG. 2.
FIG. 3 shows the configuration of the transformer 12. The primary winding set 121 and the secondary winding set 122 are respectively wound around two sides 311 and 312 of the magnetic core 123.
In the above drivers in FIGS. 1 and 2, the two winding sets of the transformer 12 are respectively used for a high-voltage side and a low-voltage side. When a plurality of lamps are driven, three methods, such as coupling the lamps in series, coupling the lamps in parallel, and using a plurality of transformers, must be used. The problems of withstand voltage of the transformer, however, is not solved easily although coupling the lamps in series can overcome the problem of different currents. A balance circuit is required for coupling the lamps in parallel. Moreover, a plurality of transformers occupy more space and cost more.